Solid state electronic devices can be fabricated with conjugated organic polymer layers. Conjugated polymer-based diodes and particularly light emitting diodes (LEDs) and light-detecting diodes are especially attractive due to their potential for use in display and sensor technology. This class of devices has a structure that includes a layer or film of an electrophotoactive conjugated organic polymer bounded on opposite sides by electrodes (anode and cathode) and carried on a solid substrate.
Generally, materials for use as active layers in polymer diodes and particularly PLEDs include semiconducting conjugated polymers that exhibit photoluminescence. In certain preferred settings, the polymers exhibit photoluminescence and are soluble and processible from solution into uniform thin films.
The anodes of these organic polymer-based electronic devices are conventionally constructed of a relatively high work function metal. This anode serves to inject holes into the otherwise filled p-band of the semiconducting, luminescent polymer.
Relatively low work function metals, such as barium or calcium, are preferred as the cathode material in many structures. This low work function cathode serves to inject electrons into the otherwise empty p*-band of the semiconducting, luminescent polymer. The holes injected at the anode and the electrons injected at the cathode recombine radiatively within the active layer and light is emitted.
LED lighting can commonly be characterized by on-axis luminous intensity expressed in candela. Intensity describes the flux per solid angle radiated from a source of finite area. Furthermore, flux is the total amount of light emitted from a source in all directions. For the purpose of this invention, flux will be used to describe the brightness of LEDs.
Radiometric light is specified according to its radiant energy and power without regard for the visual effects of the radiation. Photometric light is specified in terms of human visible response according to the CIE standard observer response curve. Furthermore, in the fields of photonics and solid state physics, luminous efficacy is defined as the conversion between photometric flux, expressed in lumens, and radiometric flux, expressed in watts.
It is noted that the luminous efficacy is a function of the dominant wavelength of a specific LED lighting source. For example, an Indium Gallium Nitride (InGaN) LED shows increasing luminous efficacy from 85 to 600 lumens per watt corresponding to a shifting of the dominant wavelength from 470 to 560 nm. On the other hand, an Aluminum Indium Gallium Phosphide (AlInGaP) shows decreasing luminous efficacy from 580 to 800 lumens per watt corresponding to a shifting of the dominant wavelength from 580 to 640 nm. For the purpose of this invention, luminous efficacy at the peak transmittance of LED is referred.
Most typical prior art LEDs are designed to operate no more than 30-60 milliwatts of electrical power. More recently, commercial LEDs capable of continuous use at one watt of input power were introduced. These LEDs use much larger semiconductor chips than previous LEDs to handle the large power. In order to dissipate heat to minimize junction temperature and maintain lighting performance, these larger chips are normally mounted to a more effective thermal conductor (such as metal slugs) than previous LED structures.
Typically, the 5-watt LEDs are available with efficacy of 18-22 lumens per watt, the 10-watt LEDs are available with efficacy of 60 lumens per watt. These 10-watt LED light devices will produce about as much light as a common 50-watt incandescent bulb and will facilitate use of LEDs for general illumination needs.
Despite the prior art LED devices currently available, a need still exists for improved LED modules which can provide improved performance characteristics, such as increased heat dissipation qualities, improved manufacturing processes, and lower cost benefits. Other benefits include closer TCE match to the chip, smaller size, light weight, environmental stability, increased circuit integration capability, enhanced light reflectivity, simplified fabrication (such as co-fireability of a multilayer structure), higher yield, broader process tolerance, high mechanical strength, and effective heat dissipation. None of the prior art LEDs provide for the use of LTCC technology or the benefits associated with the incorporation of LTCC technology, which include longer device life.
Various design and configuration of the HB (High Brightness) LED chip carrier devices were provided in the prior art. However, they all presented different problems related to various functions, manufacturability, and cost. Functioning LED devices with equal or greater than 0.5 Watt and preferably 1 Watt power rating are still needed for lighting applications, including HB LED modules for LCD applications, which allow for the improvement in heat dissipation properties to improve the overall color quality of emitting light diode modules and increase the module life. The present invention has provided such materials, methods, chip carriers, and modules to allow for such an innovation in lighting technology.